Dial indicator driving arrangement



July 22, 1958 s. SPAKMAN DIAL INDICATOR DRIVING ARRANGEMENT Filed Oct. 20, 1955 INVENTOR GERT SPAKMAN BY%W AGENT United States Patent O DIAL INDICATOR DRIVING ARRANGEMENT Geert Spakman, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application October 20, 1955, Serial No. 541,794

Claims priority, application Netherlands November 20, 1954 3 Claims. (Cl. 7410.7)

The present invention relates to dial driving arrangements. More particularly, the invention relates to driving arrangements particularly for use in wireless receivers and comprising a cord drum and a helical tension spring for stretching the cord arranged on the cylindrical surface of the drum. Compared with the usual device provided with a spring arranged internally of the drum, the arrangement in accordance with the invention has the advantage that the drum may be smaller.

The fact that the spring engages the surface of the drum with some pressure so that there is friction between the drum and the spring provides difiiculty when the spring shrinks or is stretched, which difliculty increases with decrease in the diameter of the cord drum. Consequently it has been found that, when the drum diameter is decreased beyond a definite limit, the spring cannot follow the variations in length of the cord and cannot always keep the cord taut. When the drum diameter is made comparatively large, the said advantage is lost; i. e. the drum must have a determined, comparatively critical diameter.

From a structural point of view this is a large disadvantage, since in choosing the transmission ratio between the driving shaft, on which the cord is preferably wound directly, and the driven shaft a degree of freedom is lost. This disadvantage is particularly large in the usual driving arrangements for wireless receiver dials in which the pointer is driven by the driving cord; this precludes a free choice of the length of the dial.

In the dial driving arrangement of the present invention, this difiiculty is obviated and additional advantages are obtained. In accordance with the invention, the cord drum comprises a spring drum on which the spring is wound and a driving drum which is axially shifted relatively to the spring drum and on which and from which the cord is wound, a guiding member being provided between the last-mentioned two drums for gradual and smooth transmission of the cord from the spring drum on to the driving drum. The sizes of the diameters of these drums may be unequal.

In order that the invention may be better understood, reference is made to the accompanying drawing, wherein:

Fig. 1 is a schematic side view diagram of a preferred embodiment of the dial driving arrangement of the present invention; and

Fig. 2 is a schematic plan view diagram of the embodiment of Fig. 1.

Figs. 1 and 2 show an arrangement for driving the tuning member of a radio receiver, for example an automobile radio receiver. The driving arrangement comprises substantially a spring drum 1 on which a cord 3 is wound and a driving shaft 5 about which a few turns of the cord 3 are wound. Provision may be made on the driving shaft of a control knob 7 (shown in broken lines) and a horizontal portion of the cord 3 may carry the pointer 9 of a tuning dial 11 of the receiver. The

cord drum 1 is keyed to a shaft 13 of the tuning member (not shown) of the receiver, for example a variable capacitor.

The drum comprises two parts, a spring drum 15 on the cylindrical surface of which a helical spring 17 is arranged and a driving drum 19 (Fig. 2) of difierent diameter, in the present case of smaller diameter, on which the cord is wound or from which it is wound on rotation of the drum. One end of the spring 17 is secured to the drum 15 by means of a pin 21; the other end of said spring is connected to an end of the cord 3.

The cord is wound on the drum 15 with one turn and subsequently is guided smoothly, i. e. without sharp bends, on to the driving drum 19 by means of a guiding member shaped in the form of a helical ridge 23 formed on the drum 1. From the drum 19 the cord runs to the remote driving shaft 5 and back to the drum 19 to which the second end 25 of the cord is secured.

The diameters of the drums 15 and 19 may be made different, since the cord portion which is wound on and from the drum in tuning is completely situated on the driving drum 19. Consequently, the diameter of the drum 15 is made such that the spring 17 is not bent excessively sharply and no excessive friction is produced when the spring is compressed or stretched, and the diameter of the drum 19 is determined by the desired length of the dial 11. It is essential that the cord 3 be guided smoothly from one drum to the other, since otherwise an excessive amount of friction will be produced.

The provision of separate drums has the additional advantage that the portions of the cord which leave the drum 1 cannot get entangled in the spring 17, and that the dimensions of the drums can be chosen in accordance with the requirements to be satisfied with respect to the spring (slight friction) and the cord (comparatively heavy friction), respectively.

While the invention has been described by means of a specific example and in a specific embodiment, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A dial indicator driving arrangement comprising a driving shaft, a first drum portion, a helical spring, means for aflixing one end of said spring to the cylindrical surface of said first drum portion, said spring being positioned to rest substantially circumferentially on the said cylindrical surface, a second drum portion axially spaced relatively to said first drum portion, a cord, means for aflixing one end of said cord to a point on the cylindrical surface of said second drum portion, means for aflixing the other end of said cord to the other' end of said spring, the intermediate portion of said cord being wound in at least a single turn on the cylindrical surface of each of said first and second drum portions and said driving shaft, and means for guiding said cord from said first drum portion to said second drum portion.

2. A dial indicator driving arrangement as claimed in claim 1, wherein the diameter of said second drum portion is small relative to that of said first drum portion.

3. A dial indicator driving arrangement as claimed in claim 1, wherein said guiding means comprises a ridge of substantially helical configuration aflixed to the cylindrical surface of one of the said drum portions at points adjacent the other of said drum portions.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTION I Patent No. 2,844,039 July 22, 1958 Geert Spakman i It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

In the heading to the printed specification, lines 8 and 9, for "Claims priority, application Netherlands November 20, 1954" read Claims priority, application Germany November 20, 1954 m,

Signed and sealed this 2nd day of December 1958,

( A Attest:

KARL HLAXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents 

